Issue configuring options in ASP.NET Core 2

Question

While configuring Options on my project I came up across this error :

System.InvalidOperationException: Could not create an instance of type 'Microsoft.Extensions.Options.IOptions`1[[myproject.Models.ConnectionStrings, ]'. Model bound complex types must not be abstract or value types and must have a parameterless constructor. Alternatively, give the 'optionsAccessor' parameter a non-null default value.

Any idea ?

I configured the model as following :

namespace myproject.Models
{
  public class ConnectionStrings
  {
    public ConnectionStrings()
    {
        AzureStorageConnectionString = "azurestorageconnectionstring_ctor";
    }
    public string AzureStorageConnectionString { get; set; }
  }
}

Startup.cs ConfigureServices(IServiceCollection services) contains the following two lines

services.AddOptions();
services.Configure<ConnectionStrings>(Configuration.GetSection("ConnectionStrings"));

My controller contains this

private ConnectionStrings _connectionStrings;
public IActionResult Index(IOptions<ConnectionStrings> optionsAccessor)
{
  _connectionStrings = optionsAccessor.Value;
  return View();
}

And both my appsettings.json and appsettings.Development.json consist of the following

{
 "Logging": {
 "LogLevel": {
   "Default": "Debug",
   "System": "Information",
   "Microsoft": "Information"
  }
 },
 "ConnectionStrings": {
   "AzureStorageConnectionString": "xxxxxxxxx"
 },
}

Answer 1

You're supposed to inject IOptions<ConnectionStrings> into the controller's constructor , not into the Index() method.

By defining it as an action parameter, you're expecting the ModelBinder to construct it for you (and obviously, it cannot).

See Documentation